This invention relates to lubricating compositions. Because of their thermal stability, perfluorinated polyalkylether fluids have great potential for use as engine oils, hydraulic fluids and greases. However, a serious drawback in their use results from the fact that certain metals, i.e., those likely to be present in aircraft engine components, are corroded by these fluorinated fluids at elevated temperatures in an oxidative environment. For example, when the fluids are utilized as lubricants for mechanical components composed of mild steels, serious corrosion has occurred at temperatures of about 550.degree. to 600.degree. F. Stainless steels, titanium and titanium alloys are attacked by the fluids at a temperature of about 600.degree. F. Moreover, at elevated temperatures, particularly in an oxidizing atmosphere, the fluids themselves undergo considerable degradation, to the detriment of continued lubricating capacity.
An ideal lubricant composition would be one having a relatively constant viscosity such that it is flowable or pumpable over a wide temperature range, e.g., from about -50.degree. F. to about 600.degree. F. In general, base fluids available heretofore have either had a satisfactory viscosity at low temperatures, but degraded at elevated temperatures, or, were stable and had a satisfactory viscosity at elevated temperatures, but were too viscous to flow or pump at subzero temperatures. Consequently, it has been necessary to make compromises in the selection of base fluids dependent upon the use conditions to be encountered. Such compromises have not been entirely satisfactory.
In U.S. Pat. No. 3,393,151, issued to one of us as a coinventor on July 16, 1968, lubricants are disclosed that comprise a perfluorinated aliphatic polyether and a perfluorophenyl phosphorus compound. In U.S. Pat. No. 3,499,041, issued to one of us on March 3, 1970, certain perfluoroaryl phosphines are disclosed as being anticorrosion additives for perfluorinated fluids. In U.S. Pat. No. 3,483,129, issued to one of us as a coinventor on Dec. 9, 1969, certain perfluorinated phenoxyphenyl phosphines are disclosed as being anticorrosion additives for perfluorinated fluids. In U.S. Pat. No. 3,567,802, certain perfluoropolyoxoalkane-substituted phosphinates are disclosed as being useful as corrosion and degradation inhibitors for perfluorinated fluids. In U.S. Pat. No. 4,011,267, issued to use as coinventors on Mar. 8, 1977, certain fluorinated phosphines are disclosed as being anticorrosion and antioxidation additives for perfluorinated fluids. While the phosphorus compounds described in these patents exhibit corrosion inhibiting properties, at low temperatures most of these compounds are only poorly soluble in fluorinated fluids. Also, certain members of the classes of phosphorus compounds possess high volatility characteristics for long term high temperature applications. Because of these limitations, fluorinated fluids containing such anticorrosion additives are not completely satisfactory for use in long term, wide temperature range applications.
It is an object of this invention to provide a lubricant composition which has little if any corrosive effect upon ferrous alloys.
Another object of this invention is to provide a lubricant composition which has a relatively constant viscosity over a wide temperature range.
Other objects and advantages of the invention will be apparent to those skilled in the art upon consideration of the following disclosure.